1. Field of the Invention
The present invention relates to an anti-cornea-collapsing device for ophthalmic surgery using the ultra-high vacuum aspiration.
2. Prior Art
It is vitally important to maintain the intraocular pressure (hereinafter referred to as IOP) at an appropriate level during ophthalmic operations by controlling the irrigation and/or aspiration capacity, thus preventing, in particular, cornea from collapsing. The collapse occurs when the system fails to supply sufficient inflow to the eye that compensates for the aspirated amount of liquids and/or tissues, so giving a negative vacuum surge.
Lately, KPE has widely been applied for cataract operations. KPE is the emulsification of opacified nuclei with a needle (ultrasound tip) which is oscillated by a very high frequency ultrasound energy while seizing the nuclei securely with aspiration, thus removing them out of the eye through the needle. The harder the nuclei are, the higher aspiration pressure is need for effective phacofragmentation. In case the aspiration pressure is insufficient, the ultrasound tip often fails to seize the nuclei before they break. Further, the aspiration level at the ultrasound tip starts to rise when the attracted nuclei occlude the tip.
Heretofore, in order to maintain the IOP at an appropriate level during an operation, one method is known that an irrigation bottle is positioned about 65 centimeter high above the patient's eye and then the aspiration capacity is so determined as to meet the irrigation capacity: and according to another method the desired aspiration capacity is first determined and then the height of an irrigation bottle is positioned to meet the aspiration capacity.
Some machines provided for carrying on the latter method into practice are programmed to electrically adjust the height of an irrigation bottle to the desired level to get the appropriate inflow; while several bottles with different heights are incorporated in the identical irrigation line so that one of the irrigation bottles can work to optimize the irrigation capacity by opening its valve and closing other valves.
However, when the highly positioned irrigation bottle is needed to meet the high vacuum aspiration, the irrigating amount and pressure are increased during operation; hence, sometimes it gives pain to the patients.
The Vacuum Surge Suppresser (hereinafter referred to as VSS) has been disclosed as prior art. It is a silicone-made, domed control valve which is incorporated in the aspiration line--not the irrigation line--between the outlet of the ultrasound handpiece and the aspiration inlet so the valve constricts when the suction pressure rises.
The VSS valve is designed to reduce the outflow by narrowing or blocking the aspiration line which results from collapsing of the VSS valve itself: the said collapsing of the VSS occurs after a sudden rise in the suction pressure in the aspiration line as a result of a nucleus occlusion at the aspiration port of the ultrasound tip. When the nuclei are finally sucked in and the aspiration line is freed from occlusion, the aspiration flow bursts momentarily; hence, without application of the VSS valve, the anterior chamber would collapse.
An invention published under U.S. Pat. No. 1,207,059 has provided a system for irrigation and aspiration, liquid pressures, and flow control. Another invention published under U.S. Pat No. 4,322,715 has provided a system which may optimize the irrigation and aspiration capacity during surgery, works to emulsify, seize and aspirate the nuclei safely and effectively, by selecting one of the preprogrammed parameter-combinations comprising a ultrasound energy level, irrigation bottle height, aspiration flow rate, and preset suction pressure.
As explained above, when the maximum aspiration pressure is preset high enough to improve the effect of phacofragmentation and aspiration, the aspiration pressure rises due to a nucleus occlusion at the aspiration port of the ultrasound tip while at the occlusion break, the aspiration flow bursts momentarily as the aspiration pressure increases. As a consequence, the irrigation capacity turns out insufficient, thereby causing the cornea to collapse.
For the purpose of preventing the cornea from collapsing due to anterior chamber instability the above-referred VSS being incorporated in the aspiration line at the outlet of the ultrasound handpiece, is so designed that its domed silicone valve constricts as the aspiration pressure rises, thereby narrowing or blocking the aspiration line to control the aspiration flow.
However, the silicone-made valve takes a long time to collapse due to the rigidity of silicone: the higher the aspiration pressure is set, the longer time valve takes to reach the desired level. Further, once the valve has collapsed, the aspiration outflow pronouncedly decreases, and it takes some time for the valve to restore to its original shape after collapsing.
Such disadvantages of the VSS system adversely affect the efficiency of continuing nuclei aspiration, and render the system unsuitable for efficient ophthalmic vacuum surgery . Furthermore, since the outflow decreases as the VSS valve collapses, the system fails to aspirate and seize the nuclei effectively, taking longer time for phacoemulsification; that is to say, the VSS is disadvantageous to the extent that the harder the nuclei are, the more ultrasound energy is consumed. The manner in which the VSS valve collapses is not always regular, so the aspiration flow rate can in no way stay even, either.
Heretofore, the prior art has provided either an electric elevator changing the height of the irrigation bottle, or a circulation line system automatically adjusting the amount of irrigation to meet the aspiration pressures and outflows for controlling the IOP. The electric elevator is disadvantageous because if the bottle is positioned high to increase the inflow, the irrigation pressure rises to the extent that patients may feel pains. Higher irrigation pressure causes turbulence inside the eye making it difficult to aspirate the floating nuclei quickly.
These systems usually require functions to store the parameter-combinations of the irrigation and aspiration levels to immediately obtain the desired capacity for stable anterior chamber; thus making the systems electrically and mechanically complicated, incurring high cost of production, and requiring periodical surveillance and maintenance service.